1. Field of the Invention
This invention relates to improvements in equipment used in connection with anesthesia machines and methods for use of such improved equipment. More particularly, it relates to an apparatus and method that eliminates the need to disable the anesthesia-dispensing capability of an anesthesia machine when it is configured to dispense oxygen only to a patient.
2. Description of the Prior Art
Anesthesia machines are capable of dispensing both oxygen and anesthesia (usually nitrous oxide) to patients. They may also be used to deliver oxygen only, but for safety reasons they are not designed to deliver anesthesia only. Typically, they include a main outlet dedicated to supplying a mixture of anesthesia and oxygen to a patient; an elongate flexible supply tube extends from said main outlet to a facemask that is fitted over the patient's nose and mouth to deliver the anesthesia/oxygen mixture to the patient's lungs. An elongate flexible return tube extends from the facemask to the machine and returns exhaled carbon dioxide and other gases to the machine.
When the facemask is in position over the patient's nose and mouth, the machine can be set to deliver any mixture of nitrous oxide and oxygen to the facemask. Importantly, the nitrous oxide is entrained by the oxygen flow, i.e., if oxygen does not flow, the nitrous oxide cannot flow.
There are many operations, such as eye operations, that do not require general anesthesia. A local anesthetic is generally used in such situations, and the patient remains conscious throughout the surgical procedure. Due to the uncertainties inherent in any use of general anesthesia, the use of local anesthetics is usually preferable. Patients under local anesthesia are usually given oxygen from the anesthesia machine, but the facemask is not used in those situations, such as eye surgery, because it would physically interfere with the surgical procedures. In such situations, an elongate nasal oxygen catheter is employed; such a catheter has a proximal end in fluid communication with the machine and further has a pair of nasal prongs at its distal end that are fitted into the patient's nostrils. When a nasal catheter is used, oxygen from the machine is delivered to the patient and no appreciable obstruction to the surgical procedure is presented.
A major shortcoming of the known anesthesia machines is that their parts must be reconfigured when a patient is to receive oxygen only from the machine; such reconfiguration disables the anesthesia-dispensing capability of the machine and such disabling can have catastrophic consequences.
The reconfiguration procedure includes the steps of adding an elbow member to the machine and attaching the proximal end of an elongate nasal oxygen catheter to said elbow so that oxygen from the machine that would normally flow to the patient through the main supply tube and hence to the facemask is re-routed through the elbow into said nasal oxygen catheter. Significantly, since the flow of oxygen is diverted to the elbow and the catheter, no nitrous oxide can be delivered to the patient. Thus, whenever a patient is receiving oxygen through a nasal catheter, the anesthesia-dispensing capability of the anesthesia machine is nonfunctional.
If the patient becomes uncomfortable because the local anesthetic is inadequate, it takes several minutes (usually about three minutes) to reconfigure the anesthesia machine so that it can supply nitrous oxide to the patient. During the three minute reconfiguration, the patient may suffer pain, may complain loudly, and may even become belligerent. Some patients stand up on the operating table, some attempt to leave the operating room, and so on. Under these conditions, the anesthesiologist needs to put the patient under general anesthesia quickly.
Changing the anesthesia machine from an oxygen-only mode to its anesthesia and oxygen mode is time-consuming because the elbow member must be removed from the machine, the oxygen hose must be reattached to the machine, the prongs at the distal end of the catheter must be removed from the patient's nostrils, the machine must be set to deliver the right mixture of nitrous oxide and oxygen, and the facemask must be placed into position over the patient's nose and mouth.
The existing method for delivering oxygen only to a patient has an even worse side effect. When an operation is successfully concluded by a surgical team where the patient received oxygen only and a local anesthetic, the surgical team will frequently forget to reconfigure the machine back into its anesthesia/oxygen mode, i.e., they will leave the operating theater with the elbow still attached to the machine. Thus, when the next surgical team having a patient who needs to be placed under general anesthesia uses the machine, a crisis will erupt when the surgical team notices that the patient is exhibiting the symptoms of oxygen deprivation, even though the facemask is in place and the anesthesia machine appears to be functioning normally. In the course of a frantic search for the cause of the apparent malfunction of the anesthesia machine, a member of the team will eventually notice that the elbow member is hooked up and that all of the machine's oxygen is being pumped into the room, bypassing the machine and hence preventing the flow of anesthesia and oxygen to the facemask. The elbow will then be yanked out, the oxygen hose will be placed into its proper port, and the crisis will end happily if the problem was found and fixed quickly enough.
Thus, there is a need for improvements in the methods of use of anesthesia machines and related equipment and there is a need for improvements in the related equipment. The improved equipment would enable a physician to switch from oxygen only to anesthesia and oxygen quickly. Just as importantly, the improved machine would not require the disconnection of the oxygen supply and the concomitant disabling of the machine's ability to dispense anesthesia at any time. Thus, subsequent users of the machine would never need to reconfigure it in order to avoid problems.
However, at the time the present invention was made, it was not obvious to those of ordinary skill in this art how the known methods of use of anesthesia machines could be improved, and how the related equipment could be made better.